Electron discharge apparatus



March 12, 1 940.

E. BRUCE ELECTRON DISCHARGE APPARATUS Filed March 31, 1937 2Sheets-Sheet l I 1 II I I l l I I 1 'l NEGAT/l ECUNTROL GRID I OL7J4 E//v VEN TOR By E. BRUCE ATTORNEY Patented Mar. 12, 1940 UNITED STATESFFlE ELECTRON DISCHARGE APPARATUS Application March 31, 1937, Serial No.134,008

decrease in the negative grid potential produces 12 Claims.

This invention relates to electron discharge apparatus and moreparticularly to such apparatus including multi-grid electron beamdischarge devices and especially suitable for the detection,amplification and generation of ultrahigh frequency impulses.

One object of this invention is to enable the attainment of a markeddepression in the mutual conductance characteristic of an electrondischarge device so that for certain values of electrode potentials theanode current of the device decreases and then increases with successiveincrements in the potential of the control electrode or grid.

Another object of this invention is to reduce the anode to ground andanode-control electrode capacities in electron discharge devices.

A further object of this invention is to augment the control of theanode current by the control electrode or grid in electron dischargedevices.

In one illustrative embodiment of this invention, electron dischargeapparatus comprises an electron beam discharge device having a cathode,a pair of spaced grid electrodes surounding the cathode and an anodeoutside of the outer grid electrode. The grid electrodes may comprise aplurality of spaced linear elements parallel to each other and thecathode, the corresponding elements of the two grid electrodespreferably being in radial alignment with one another and with thecathode.

The outer grid electrode may be maintained at a suitable negative biaswith respect to the oathode and utilized to control the magnitude of theelectron streams from the cathode to the anode; The inner grid electrodemay be maintained at a positive potential lower than the anodepotential, with respect to the cathode and utilized pri- 40 marily as anaccelerating electrode.

In acordance with one feature of this invention, the anode includes aplurality of linear elements mounted parallel to one another and to thecathode, each of the anode elements being in alignment with the cathodealong a radius bisecting the space between successive correspondingelements of the grid electrodes. It has been found that in apparatusconstructed in ac cordance with this invention, the anode current variesin a novel manner with respect to the potential upon the controlelectrode or grid. Specifically, it has been found that as the controlelectrode or grid is made less negative from a high negative value, theanode current increases somewhat gradually to a maximum. A furthermarked decrease in the anode current. This latter effect occursthroughout a limited range of grid potentials and the anode currentreaches a minimum. As the grid is made still less negative, the anodecurrent again increases.

Hence,

a marked depression occurs in the anode currentcontrol grid potentialcharacteristic of the devicel In accordance with another feature of thisinvention, the fixed potentials upon the several electrodes are madesuch that the device operates about a point in the depression occuringin the anode current-grid potential characteristic.

For

The invention and the various features thereof will be understood moreclearly and fully from the following detailed description with referenceto the accompanying drawings in which:

Fig. 1 is a View in perspective of an electron discharge deviceconstructed in accordance with this invention, a portion of theenclosing vessel and of the electrode assembly being broken away to showdetails of construction more clearly;

Fig. 2 is a view in cross-section along line 2 2 of Fig. 1, of theelectrode assembly, illustrating the construction, configuration andarrangement of the various electrodes;

Fig. 3 is a graph showing the relation between the anode current and thenegative control grid voltage in devices of the construction illustratedin Figs. 1 and 2;

Figs. 4 and 5 are diagrammatic views illustrating typical pathstraversed by electrons emanating from the cathode in devices of theconstruction shown in Figs. 1 and 2;

Fig. 6 is a schematic of a typical circuit illustrating the utilizationof apparatus constructed in accordance with this invention as adetector, amplifier, or frequency doubler;

Fig. '7 is a circuit diagram of a feedback oscillator illustrative ofone embodiment of this invention; and

Figs. 8 and 9 are circuit diagrams of other oscillators illustrative ofthis invention.

Referring now to the drawings, the electron discharge device shown inFigs. 1 and 2 comprises an evacuated enclosing vessel it having a stem ll at one end and having suitably aflixed thereto a arising therefrom areparallel,

base i2 carrying terminal prongs 13 through which the electrodes of thedevice may be associated with external circuits.

Embedded in the press i l of the stern i! and rigid, metallic supportsor uprights l5, one of which is connected electrically to one of theterminal prongs is by a leading-in conductor it. An insulating disc ii,for example, of mica, is affixed to the supports or uprights l5 adjacentthe upper end thereof, as by clips 18 which may be welded to theuprights or supports. Similar spaced insulating discs i9 and 20, whichalso may be of mica or the like, are aifixed to the supports or uprights55 by suitable clips 2!, which also may be welded to the uprights orsupports.

An elongatedlinear cathode, which may be either a filament or of the euipotential heater type, is supported between the insulating discs ll,l0 and 28. In the form shown in Figs. 1 and 2, the cathode comprises acylindrical metallic sleeve 22, coated on its outer surface with athermionic material, one end of which extends through and is fitted incentral apertures in the lower insulating discs it and 2t and the otherend of which is reduced, as indicated at 23, and fitted in a centralaperture in the upper insulating disc H. The cathode sleeve 22 enclosesa heater filament 25 embedded in or threaded through a suitable ceramicor insulating body 25. Heating current may be supplied to the filament2=i through leading-in conductors 26 embedded in the press H5 andconnected to corresponding ones of the terminal prongs i3. Electricalconnection to the cathode 22 may be established through a leading-inconductor 22'! also embedded in the press i i and connected to one ofthe terminal prongs iii.

The cathode 22 is surrounded by an accelerating electrode or gridcoam'al therewith and including a plurality of equally spaced linearconductors or wires 28 mounted parallel to one another and to thecathode. The conductors 28 extend through aligned apertures in theinsulating discs 51, i9 and 2E and are electrically connected to oneanother by a metallic band or 001- lar 29 seated upon the insulatingdisc Zil. One of the conductors may be connected to one of the terminalprongs it through a leading-in conductor 3Q embedded in the press M.

The accelerating electrode or grid 23 is encompassed by a controlelectrode or grid, preferably coaxial therewith, which comprisesaplurality of parallel, linear conductors or wires 35 each of which, asshown clearly in Fig. is in radial alignment with the cathode 22 and acorresponding one of the wires 28 of the inner grid. The conductors orwires 35 extend through aligned apertures in the insulating discs ll, l9and 2t and are connected together electrically by a metallic band orcollar 32 seated upon the in sulating disc 2i Suitable potentials may beapplied to the control electrode through a leadingin conductor 33connected to one of the conductors or wires 3% and to one 01 theterminal prongs I3.

The control electrode or grid Si is encompassed in turn by an anode,coaxial therewith, which comprises a plurality of parallel, linear rodsor wires 35 each of which, as shown clearly in Fig. 2, lies on a radiuspreferably bisecting the opening between successive accelerating gridwires 28 and the corresponding control grid wires 35. The anode wires orconductors 3 extend through aligned apertures in the insulating discs H,is

and 20 and are electrically connected by a metallic band or collar 35seated upon the disc 20. The anode may be coupled to an external circuitthrough a leading-in conductor 38 connected to one of the terminalprongs l 3 and to one of the conductors or wires 34.

The anode may be encompassed in turn by an auxiliary electrode having acylindrical portion 3? and diametrically opposite flanges 38 which maybe secured, as by welding, to the uprights or supports 15.

During operation of the device, as shown in Fig. 6, an input circuitincluding a network 39 and a source, such as a battery :26, for applyinga negative bias to the control electrode 3!, is connected between thecathode 22 and the control electrode. An output system ii may heeonnected across a suitable resistance 42 connected between the cathode22 and anode 34 in series with a suitable source, such as a battery 3,for applying a positive potential to the anode. The acceleratingelectrode 28 may be connected to an intermediate terminal on the battery4! so that it is at a positive potential, lower than the anodepotential, with respect to the cathode. Preferably, the fixed potentialsapplied to the several electrodes are such that the electrons emanatingfrom the cathode are concentrated in beams focussed upon the anode wires34. The auxiliary electrode 31, not shown in Fig. 6, may be connecteddirectly to the cathode and operated at cathode potential.

As noted heretofore, as the control electrode potential is made lessnegative, the anode current ihst increases, then decreases, andsubsequently again increases. As shown in Fig. 3, for values of negativecontrol grid voltage between A and B, as this voltage becomes lessnegative, the anode current increases continuously to a maximum value c.As the grid potential is made still less negative, between values 13 andC the anode current decreases to a minimum value a. In accordance withstill further decreases in the control grid potential, as between valuesC and O, the anode current increases to a value f.

Although this invention is not to be limited thereby, the followingconsiderations are believed to explain the occurrence of the depressioncaj appearing in the mutual conductance characteristic shown in Fig. 3.Referring to Fig. 4, the circles designated by the numerals l to 3,inclusive, represent electrons having a charge q emanating from spacedportions of a cathode, not shown, and propagated with a uniformvelocity 1) toward the anode wire 34 under the infiuence of thepotentials upon the anode and the accelerating and control electrodes orgrids.

Electron I will traverse a path M perpendicular to the longitudinal axisof the anode wire 34 and hence will flow directly to the anode wire 34contributing thereby to the anode current. Electron 2, however, havingthe same charge and velocity as electron I, will follow a path N andattempt to pass the anode wire 34 at a distance d: from the axisthereof. When this electron approaches the anode wire it comes under apowerful deviatingforce, due to the anode potential, normal to the pathN. Consequently, the electron 2 will then traverse a curvilinear path,as indicated for example by the line N1, and eventually reach the anodewire 34.

The electron 3 will traverse a path P and attempt to pass the anode wire36 at a distance d3 from the axis thereof where the deviating force dueto the anode potential is less han that acting upon the electron 2.Consequently, the path of the electron 3 will become curvilinear asindicated in part by the line P1 and this electron may eventually reachthe anode.

The velocity of certain of electrons emanating from the cathode and thedeviating forces acting thereon will be such that the resultingcentrifugal force is substantially equal to the deviating force.Consequently, such electrons will traverse a substantially circularpath, as indicated for example by the lines P1 and P2 in Fig. 5,concentric with the anode wire 34, and constitute an electron shieldabout the anode wires.

The force upon other electrons may be such that these electrons neverreach the anode. For example, such electrons may reverse their directionof travel and flow to the accelerating elec trode 28 as indicated by thelines R in Fig. 5. Still other electrons may flow directly to theaccelerating electrode 28 as indicated by the lines S in Fig. 5.

The paths traversed by the electrons, of course, will be dependent uponthe velocities of the electrons as they approach the anode and thesevelocities in turn are dependent upon the potential of the controlelectrode or grid. For high negative values of the control gridpotential, such as indicated for example by the abscissae between A andB in Fig. 3, the electron velocities will be relatively small with theresult that most of the electrons emanating from the cathode 22 willflow directly to the anode 34. Consequently, the anode current willincrease up to a point 0 in Fig. 3 as the grid is made less negative.

As the grid is made still less negative, the velocities of certain ofthe electrons will increase and these electrons will rotate about theanode wires as heretofore described with the attendant establishment ofan electron shield about the anode wires. The density and effectivenessof this electron shield will increase as more electrons flow toward theanode wires and circulate thereabout, so that, as indicated by theportion cc of the curve in Fig. 3, the anode current will decrease.

As the control grid is made still less negative, the electron velocitiesincrease with the result that a relative large radius for the circle ofrotation of certain of the electrons is established and, therefore, theshielding effect decreases..

The orbits of rotation may even exist beyond the confines of the denserpart of the electron stream focussed upon the anode wires 34.Consequently, the anode current increases with decreasing grid potentialas indicated by the portion of of the curve in Fig. 3.

The critical region of the electron shield, that is the regioncorresponding to conditions extent at the time the anode current is ator near the point a indicated in Fig. 3, probably obtains when theradius of the orbits of the rotating electrons just equals the radius ofanode wires 34-, that is When Knowing the relative distribution of theelectromotive intensity along the electrons path, .the

critical velocity and the requisite electrode voltages may be estimatedby considering that the potential energy of an electron, just outside ofthe cathode surfaces, is converted to kinetic energy at the surface ofthe anode wires.

In a specific embodiment illustrative of this invention, the minimumpoint a. of the anode current has been obtained at a potential of 2.5volts upon the control grid, the anode and accelerating electrode being60 volts and 18 volts positive respectively, the accelerating andcontrol electrodes having radii of 0.07 inch and 0.13 inch respectively,the anode wires lying in a circle having a radius of 0.19 inch and thecylindrical auxiliary electrode defining a boundary 0.25 inch in radius.

It will be appreciated, of course, that in devices constructed inaccordance with this invention, because of the relatively small anodearea, relatively small capacitances between the anode and ground andbetween the anode and the control grid will exist. Furthermore, it willbe seen that in addition the usual control of the density of theelectron streams by the control grid is augmented inasmuch as the focalpoint of the electron streams is varied in accordance with variations inthe potential of the control electrode so that it may be displaced fromthe anode wires 34 to points nearer or more remote from the cathode 22.

The novel characteristics of electron discharge apparatus constructed inaccordance with this invention may be utilized advantageously in avariety of applications. For example, the system shown in Fig. 6 may beused as a low frequency detector in which case the control grid isbiased at the point C in Fig. 3, the element 39 would be a radiofrequency amplifier and the element ti an audio amplifier. In suchapparatus the anode current would increase with both positive andnegative swings of the potentials impressed upon the control grid.

Similarly with the control grid biased at the point C, Fig. 3, frequencydoubling accompanied by large amplification and high suppression of thefundamental frequency may be obtained. In such application, the element39 would be an input frequency device and the element 4| would be anoutput doubled frequency device.

The system shown in Fig. 6 may be utilized also as an amplifier, havingin addition to a high mutual conductance a negative feedback through theanode-control grid capacitance. In this system, the control grid wouldbe biased at values corresponding for example to the point D in- Fig. 3,and the elements 39 and M would be suitable input and output devicesrespectively.

Fig. '7 illustrates a feedback oscillator illustrative of one embodimentof this invention, wherein an anti-resonant element including a variablecondenser 45 and inductance 46 in shunt therewith is provided common tothe control grid and anode circuits. The control grid 3! is biased at apoint between B and C, Fig. 3 and the po-v tentials upon the anode andaccelerating electrode are such that a positive anode resistance and anegative amplification factor exist.

The potentials upon thhe electrodes may be made such that a negativeanode resistance is exhibited. Hence, feedback is not necessary togenerate oscillations. In such case the grid 3! should be biased at apoint between B and C, Fig. 3, and preferably at a value correspondingto point I) on the characteristic. Oscillators wherein the electrodepotentials are thus related are illustrated in Figs. 8 and 9. In Fig. 8the shunt condenser-inductance element is connected between the cathodeand anode; in Fig. 9, this element is connected between. the controlgrid and the cathode.

In Figs. 6 to 9, the auxiliary electrode 31 has not been shown inasmuchas it has been found that the characteristics described hereinabove maybe achieved without the use of such electrode. It may be employed,however, to prevent escape of the electrons materially beyond theconfines of the anode and in such case is operated at cathode potential.

Although various embodiments of this invention have been shown anddescribed it will be understood, of course, that various modificationsmay be made therein without departing from the scope and spirit of thisinvention as defined in the appended claims.

What is claimed is:

1. Electron discharge apparatus comprising a cathode, an anode having aslender linear electron receiving member, a grid between said cathodeand said anode, said grid and anode being separated only by space, anoutput circuit connected between said cathode and said anode, and aninput circuit for impressing variable potentials between said gridandsaid cathode, said in put circuit including means for impressing sucha negative bias upon said grid that the anode current increases withboth positive and negative increments in said variable potentials.

2. Electron discharge apparatus in accordance with claim 1 comprising anaccelerating electrode between said cathode and said grid and meansapplying such positive potential to said accelerating electrode thatelectron streams emanating from said cathode are substantially focussedupon said electron receiving member.

3. Electron discharge apparatus comprising a substantially linearcathode, an anode having a linear electron receiving member parallel tosaid cathode, a grid between said cathode and said anode including apair of spaced linear members parallel to said cathode and mounted atopposite sides of a line passing through said cathode and said anode,said spaced members being electrically integral, a circuit connected tosaid cathode and said anode, a second circuit connected to said cathodeand said grid, means for biasing said grid negatively with respect tosaid cathode so that the current in said first circuit increases withnegative increments in the potentials impressed upon said grid by saidsecond circuit, an accelerating electrode between said cathode and saidgrid hav ing a pair of spaced linear elements each in alignment withsaid cathode and a corresponding one of said spaced linear members, saidelements being spaced from one another a distance smaller than thespacing between said linear members, and means for maintaining saidaccelerating electrode at a positive potential with respect to saidcathode.

4. Electron discharge apparatus in accordance with claim 3 wherein saidfirst means applies such biasing potential to said grid that the anodecurrent increases with both positive and negative swings in thepotentials in said second circuit.

5. Electron discharge apparatus comprising a cathode, a grid electrodehaving spaced electrically integral members in alignment with saidcathode and substantially equally spaced therefrom, and an anode havinga linear rod electron receiving member of cross-sectional dimensionsless thanthe cross-sectional dimensions of said cathode, in alignmentwith said cathode and the opening between two of said spaced members,said grid electrode being between said cathode and said anode, and saidgrid electrode and anode being separated only by space.

6. Electron discharge apparatus comprising a cathode, a pair ofcylindrical grids coaxial with said cathode, each of said grids having apltu'ality of spaced rod elements parallel to each other and thecorresponding elements of said grids being arranged in alignment withone another and said cathode, and an anode surrounding said grids andincluding a plurality of slender spaced conductors parallel to saidcathode, said conductors being in radial alignment only with saidcathode and with the openings between successive elements of said grids,and the cross-sectional dimensions of said conductors being small incomparison with the spacing between successive rod elements of the outerof said grids.

7. Electron discharge apparatus comprising a cathode, a controlelectrode including a plurality of spaced members parallel to oneanother and said cathode and arranged in a cylindrical boundary coaxialwith said cathode, a cylindrical accelerating electrode between saidcathode and said control electrode and coaxial therewith, saidaccelerating electrode including a plurality of linear elements each ofwhich is radially aligned with a corresponding one of said spacedmembers, said mem ers being electrically connected together, and ananode surrounding said control electrode including a plurality of spacedslender linear conductors mounted parallel to one another and thecathode, each of said conductors being in alignment with said cathodeand an opening between two of said spaced members, and the portions ofsaid control electrode between said cathode and anode consisting of saidspaced members.

8. Electron discharge apparatus in accordance with claim 7 comprising acircuit coupled to said cathode and said anode, and a second circuitcoupled to said cathode and said control electrode and including meansfor biasing said control electrode negatively with respect to saidcathode such that the anode current varies directly with variations inthe negative potential of said grid.

9. Electron discharge apparatus in accordance with claim '7 a circuitcoupled to said cathode and said anode, a second circuit coupled to saidcathode and said control electrode and including means for applying anegative bias to said control electrode, and means for maintaining saidaccelerating electrode at a positive potential with respect to saidcathode, said negative bias and positive potential being such thatelectrons emanating from said cathode form streams substantiallyfocussed upon said conductors of said anode.

10. Electron discharge apparatus comprising a linear slender wire anode,means for producing a stream of electrons directed toward said anodecomprising an electrode system including a cathode and a controlelectrode, said control electrode being between said cathode and saidanode, the outermost electrode or said system and separated from saidanode only by space, a circuit coupled to said cathode and said anode,and a circuit connected to said cathode and said control electrode andincluding means for biasing said control eletrcde at such a negativepotential that the anode current varies directly with variations in thepotential of said control electrode throughout a range of negativevalues of control electrode potential.

11. Electron discharge apparatus in accordance with the preceding claimwherein said first means includes an auxiliary electrode between saidcathode and said control electrode and means for maintaining saidauxiliary electrode at such potential that said auxiliary electrodetogether with said control electrode defines an electronic lensfocussing the electron stream upon said anode.

12. Electron discharge apparatus comprising a cathode, a linearcylindrical rod anode, an output circuit coupled to said cathode andanode, means for accelerating the electrons emanating from said cathode,and means for controlling the velocity of the accelerated electronsincluding a control electrode biased negatively with respect to saidcathode at such potential that the current in said circuit variesdirectly with increments in the potential of said control electrode.

EDMOND BRUCE.

